iwlwifi: mvm: Report tx/rx antennas

This makes it easier for user-space to know how many antennas the
radio has.  Seems to work with the AX200 radio, at least.

Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>